1. Field of the Invention
The present invention relates to an image forming apparatus including a contact/separation mechanism to/from an intermediate transfer body, and to a method of confirming an operation of the contact/separation mechanism in the image forming apparatus.
2. Description of the Related Art
In a four-cycle color printer as a conventional image forming apparatus performing color printing, an intermediate transfer belt as an intermediate transfer body is rotated four times to form a color image on the intermediate transfer belt. Specifically, toner images of yellow (Y), magenta (M), cyan (C) and black (K) are formed superposed on the intermediate transfer belt, and transferred to a sheet of paper, so that a color image is printed on the sheet of paper. Thereafter, in the four-cycle color printer, a cleaner (also referred to as a belt cleaner) is brought into contact with the intermediate transfer belt to scrape off toner left of the intermediate transfer belt, and then, a toner-image of yellow (Y) for the next printing is formed on the intermediate transfer belt. By the time when the intermediate transfer belt rotates and the position of the intermediate transfer belt on which the yellow (Y) toner image is formed reaches the position at which the cleaner is arranged, the cleaner is separated from the intermediate transfer belt. Thereafter, toner images of respective colors, that is, magenta (M), cyan (C) and black (K), are formed superposed on the intermediate transfer belt. For this purpose, the four-cycle color printer is provided with a mechanism for bringing the belt cleaner into contact with and separate from the intermediate transfer belt.
The mechanism for bringing the belt cleaner into contact with and separate from the intermediate transfer belt (also referred to as a cleaner contact/separation mechanism) is provided with a sensor. The sensor detects whether the belt cleaner is in contact with or separated from the intermediate transfer belt. A mechanism controlling the cleaner contact/separation mechanism controls contact/separation of the belt cleaner based on the sensor signal from the sensor. Further, based on the sensor signal, it detects abnormality of contact/separation of the belt cleaner with respect to the control, and detects any error of the cleaner contact/separation mechanism.
In a tandem type color printer as a conventional image forming apparatus performing color printing, four photoreceptors corresponding to respective colors, that is, yellow (Y), magenta (M), cyan (C) and black (K) are arranged facing to the intermediate transfer belt. In the tandem type printer, for color printing, all photoreceptors (Y, M, C, K) are brought into contact with the intermediate transfer belt and toner images of respective colors are transferred to the intermediate transfer belt. For monochrome (black) printing, photoreceptors for color printing (Y, M, C) (hereinafter referred to as color photoreceptors) are separated from the intermediate transfer belt. Only the photoreceptor for monochrome printing (K) that is in contact with the intermediate transfer belt is driven. As a result, a monochrome toner image is transferred to the intermediate transfer belt. Thus, the tandem type color printer is provided with a mechanism for bringing the color photoreceptors into contact with and separate from the intermediate transfer belt.
The mechanism for bringing the photoreceptor into contact with and separate from the intermediate transfer belt (also referred to as a photoreceptor contact/separation mechanism) is provided with a sensor. The sensor detects whether the photoreceptor is in contact with or separated from the intermediate transfer belt. A mechanism controlling the photoreceptor contact/separation mechanism controls contact/separation of the photoreceptor based on the sensor signal from the sensor. Further, based on the sensor signal, it detects abnormality of contact/separation of the photoreceptor with respect to the control, and detects any error of the photoreceptor contact/separation mechanism.
As described above, both the four-cycle color printer and the tandem type color printer include contact/separation mechanisms to/from the intermediate transfer belt. Therefore, in either of the mechanisms, a sensor for detecting the contact/separation operation has been necessary.
Cost reduction of such image forming apparatuses has been demanded. The sensor mentioned above, however, is one of the factors hindering cost reduction. By way of example, Japanese Laid-Open Patent Publication No. 2006-337798 discloses a method of determining contact/separation of belt cleaner to/from the intermediate transfer belt, by forming a toner patch on the intermediate transfer belt and detecting the toner patch using a density sensor, in a four-cycle color printer. By adopting this method, a sensor for detecting the contact/separation operation of the belt cleaner to/from the intermediate transfer belt becomes unnecessary in the four-cycle color printer. As a result, cost can be reduced.
In the method described in the afore-mentioned application, the intermediate transfer belt is rotated and after the position where the toner patch is formed passes through the position of belt cleaner, the density of toner patch is detected by the density sensor. Therefore, detection of the contact/separation operation of belt cleaner to/from the intermediate transfer belt takes time to rotate the intermediate transfer belt to have the toner-patch-formed position moved from the exposure/development position to the belt cleaner position and time to rotate from the belt cleaner position to the density sensor position. Namely, it takes time to rotate the intermediate transfer belt almost twice.
Further, at the time of power-on, for example, whether the belt cleaner is in the contact state or separate state is unknown. Therefore, in order to confirm intactness of contact/separation mechanism or to confirm that the mechanism operates normally both from the contact state to the separate state and from the separate state to the contact state, it is necessary to operate the contact/separation mechanism to form a toner patch on the intermediate transfer belt, and to operate the contact/separation mechanism in the reverse manner to form the toner patch again on the intermediate transfer belt. Specifically, it is necessary to perform twice the process for forming the toner patch and determining the state of contact/separation. This takes time to have the intermediate transfer belt rotated almost four times.
Therefore, according to the method disclosed in the afore-mentioned application, longer time is necessary for performing preliminary rotation and returning to the initial state and for determining any malfunction of the contact/separation mechanism thereafter. Consequently, if the state of contact/separation is confirmed to determine any malfunction of the contact/separation mechanism during printing, productivity of image forming apparatus would be decreased.
The method described in the afore-mentioned application may be applied to the tandem type color printer, and the operation of photoreceptor contact/separation mechanism may be confirmed by forming and detecting a toner patch, rather than detecting the contact/separation state of color photoreceptor by the sensor. Similar to the method applied to the four-cycle color printer, here again, longer time is necessary for performing preliminary rotation and returning to the initial state and for determining any malfunction of the contact/separation mechanism thereafter. Consequently, if the state of contact/separation is confirmed to determine any malfunction of the contact/separation mechanism during printing, productivity of image forming apparatus would be decreased.